1. Field of the Invention
The present invention generally relates to circular saws. More particularly, the present invention relates to a corner-cutting circular saw including a base plate and a saw blade assembly tiltably mounted on the base wherein when the assembly is tilted rearward, the portion of the blade protruding below the base plate pivots forward to cut a workpiece where the workpiece forms a corner with a wall or similar structure.
2. Description of the Related Art
A typical circular saw capable of cutting a workpiece such as a wooden board along a corner, for example, where the workpiece board and another board meet to form a right angle therebetween, includes a saw blade assembly which has a saw blade on a front end thereof and a motor disposed on a rear end thereof for driving the saw blade. The circular saw further includes a generally rectangular base plate below which the lower portion of the saw blade extends through a recess cut in the front side edge of the base plate. The saw blade assembly is mounted on the base plate by means of a pair of connecting shafts extending in parallel to the saw blade such that the assembly is tiltable relative to the base plate with the saw blade disposed parallel to the front side edge of the base plate. To perform ordinary bevel cutting, the lower portion of the saw blade is caused to pivot toward the motor by tilting of the assembly outward in the direction opposite to the motor (to the front of the tool). Conversely, in order to perform bevel cutting along or close to a wall or structure extending upward, for example, at a right angle to the workpiece, the lower portion of the saw blade is pivoted in the recess in the direction opposite to the motor by tilting of the assembly toward the motor (bevel cutting along or close to a wall or similar structure extending, for example, at a right angle to the workpiece is hereafter referred to as corner cutting through the specification).
The foregoing conventional saw, however, suffers from certain deficiencies that reduce its utility. Referring to FIG. 5, in the conventional electric power tool, the common axis O1 of the connecting shafts (which couple the saw blade assembly 120 to the base plate 123) coincides with or lies in the center plane L of the saw blade 122. Accordingly, when an operator tilts the saw blade assembly for corner cutting, the upper blade guard 121 covering the upper portion of the saw blade 122 rotates about the connecting shafts. As indicated by the two-dot chain lines, when the assembly is tilted to the maximum angle, whereby the saw blade 122 is located on the front edge of the base plate 123, the bottom end of the blade guard 121 protrudes beyond the perpendicular plane (P) in which the front side edge of the base plate 123 is located (the portion of the guard 121 protruding beyond the perpendicular plane P is hatched in the figure). Depending on the situation, it may not be possible to bring the base plate 123 into abutment with the wall due to the protruding portion of the upper blade guard 121, thus making corner cutting difficult or in some cases impossible. If the protruding portion or the bottom end of the blade guard 121 is cut off to avoid possible interference with a wall or other structure, the structural strength of the blade guard is compromised.
In view of the above-identified problems, an important object of the present invention is to provide a circular saw capable of corner cutting without interference with a wall or similar structure even in the maximum tilt position of the saw blade while maintaining the tool""s structural strength.
Another object of the present invention is to provide a circular saw capable of making cuts along corners without changing the design of the upper blade guard or other components of the saw blade assembly.
The above objects and other related objects are realized by the invention, which provides a circular saw capable of cutting a workpiece at a generally right-angled corner formed between the workpiece and a structure. The circular saw comprises a saw blade assembly including a motor on a rear side thereof and a saw blade on a front side thereof. The saw blade has a center plane extending therethrough and is adapted so as to be rotated by the motor. The circular saw further comprises a generally rectangular base plate having a front edge proximal to the saw blade and distal to the motor and a recess provided in the front edge through which the saw blade protrudes below the base plate. Additionally included in the circular saw are a plurality of connecting shafts having a common axis extending in parallel to both the center plane of the saw blade and the front edge of the base plate, with the connecting shafts attaching the saw blade assembly to the base plate such that the saw blade assembly is tiltable toward the rear side about the common axis of the connecting shafts, thereby causing at least the portion of the saw blade protruding below the base plate to pivot to the front side. In this circular saw, when the blade saw assembly is tilted to hold the saw blade at a right angle relative to the base plate, the axis of the connecting shafts is spaced apart from the center plane toward the motor by a predetermined distance. This arrangement ensures excellent corner cutting without interference of the saw blade assembly with walls or other structures which form a right-angle corner with workpieces. Neither is any additional change in the design or shape of the saw blade assembly required to avoid such interference.
According to one aspect of the present invention, the predetermined distance of separation between the axis of the connecting shafts and the center plane of the saw blade is approximately 1 centimeter.
According to another aspect of the present invention, the location of the common axis of the connecting shafts is selected such that when the assembly is maximally tilted to the rear side, a predetermined amount of clearance is created between the vertical plane located on the front edge of the base plate and the forwardmost part of the saw blade assembly, thus effectively preventing interference between the assembly and a structure forming a corner with the workpiece. Due to this arrangement, no part of the saw blade assembly protrudes forward from the vertical plane lying on the front edge of the base plate when the saw blade assembly is tilted, locating the entire assembly inside (i.e., to the rear of the saw) the front edge of the base plate.
According to still another aspect of the present invention, the saw blade assembly further includes an upper blade guard which covers an upper portion of the saw blade and when the assembly is maximally tilted to the rear, the forwardmost part of the saw blade assembly is a bottom end of the upper blade guard.
According to yet another aspect of the present invention, the circular saw further comprises: a lower blade guard which normally covers a lower portion of the saw blade and is retractable to expose the lower portion of the saw blade; and a grip plate which is attached to the lower blade guard and extends radially away from the saw blade along the center plane of the saw blade. The grip plate is manually operable with ease so as to retract the lower blade guard even when the front edge of the base plate is set in abutment with a structure forming an approximately 90-degree corner with the workpiece. Due to its configuration, the grip plate can be easily operated by hand even when making a corner cut in limited space without interfering with a wall or similar structure.
According to one feature of the present invention, the saw blade, when pivoted to the maximum angle, extends through the recess with a front face of the saw blade substantially intersecting the imaginary front edge of the portion of the base plate removed by the recess, while the bottom end of the upper blade guard is located on the rear side of the vertical plane that is located on the front edge of the base plate.
According to another feature of the present invention, the circular saw further includes: an auxiliary base plate including a bottom surface; a pair of guide bars secured to the auxiliary base plate at a right angle; and means for securing the guide bars to the base plate. When the auxiliary base plate is secured to the base plate, the bottom surface of the auxiliary base plate is located on the same plane as a bottom surface of the base plate and the saw blade is interposed between the auxiliary base plate and the base plate. As both the base plate and the auxiliary base plate are set on a workpiece on the front and rear sides of the saw blade, cuts can be made in a more stable manner than without the auxiliary plate.
According to still another feature of the present invention, the means for securing includes: a pair of insertion holes provided in the base plate for allowing insertion of the guide bars therethrough from the front side; a pair of threaded holes provided in the base plate in communication with the insertion holes; and a pair of thumbscrews for being tightened into the threaded holes so as to press free ends of the thumbscrews against the guide bars in the insertion holes. This permits the auxiliary base plate to be held against movement relative to the base plate.
According to yet another feature of the present invention, the auxiliary base plate further includes an front edge and, when the auxiliary base plate is secured to the base plate, the front edge of the auxiliary base plate extends in parallel to the front edge of the base plate. Due to this feature, the operator can make accurate cuts in workpieces by abutting a ruler or other suitable reference and/or measuring device against the front side edge of the auxiliary base plate.